1. Field of Invention
The present invention pertains to the field of magnetic memories. More particularly, this invention relates to providing a stabilized magnetic memory cell in a magnetic memory.
2. Art Background
A magnetic memory such as a magnetic random access memory (MRAM) typically includes an array of magnetic memory cells. Each magnetic memory cell usually includes a data storage layer and a reference layer. The data storage layer is usually a layer or film of magnetic material that stores magnetization patterns in orientations that may be altered by the application of external magnetic fields. The reference layer is usually a layer of magnetic material in which the magnetization is fixed or "pinned" in a particular direction.
The magnetization pattern in the data storage layer of a magnetic memory cell typically consists of two distinct regions of magnetization--its interior region and its edge regions. The magnetization in the interior region usually aligns with what is commonly referred to as the easy axis of the data storage layer. The magnetization in the edge regions tend to align along the corresponding edges. The overall orientation of magnetization in the data storage layer of a magnetic memory cell results from the magnetization in the interior region as well as the magnetization in the edge regions.
Typically, the state of a magnetic memory cell depends on the relative orientations of magnetization in its data storage and reference layers. A magnetic memory cell is typically in a low resistance state if the overall orientation of magnetization in its data storage layer is parallel to the orientation of magnetization in its reference layer. In contrast, a magnetic memory cell is typically in a high resistance state if the overall orientation of magnetization in its data storage layer is anti-parallel to the orientation of magnetization in its reference layer.
Typically, the logic state of a bit stored in a magnetic memory cell is written by applying external magnetic fields that alter the overall orientation of magnetization in the data storage layer. The external magnetic fields may be referred to as switching fields that switch a magnetic memory cell between its high and low resistance states. A stabilized magnetic memory cell may be defined as one that remains in its high or low resistance state until switched by a well defined switching field.
The manufacturing process for a magnetic memory commonly creates surface irregularities near the edges of the data storage layers of individual magnetic memory cells. For example, such surface irregularities may be caused by inaccuracies in the patterning steps that form the edges of the data storage layers. This effect usually becomes more pronounced as smaller elements are formed at the limit of lithography used to achieve higher storage densities in a magnetic memory. Unfortunately, such surface irregularities may render individual magnetic memory cells unstable. For example, such surface irregularities may cause magnetic patterns in the edge regions of a data storage layer which have unpredictable or random orientations and switching behavior.
One prior solution for minimizing these negative effects is to form each data storage layer as a rectangle with an elongated dimension along its easy axis. Such a structure usually increases easy axis contribution to the resulting orientation of magnetization in the data storage layer in comparison to contributions from the edges. Unfortunately, such a rectangular configuration usually requires more energy to flip the orientation of magnetization in the data storage layer during write operations, thereby causing increase power consumption in an MRAM that uses such a structure. In addition, such rectangular magnetic memory cells usually limit the overall memory cell density that may be obtained in an MRAM.